Welcome to Acronis forums! First of all, make sure you can log in to https://account.acronis.com/#/auth/login using the same credentials. If login works, check out solutions from the article https://kb.acronis.com/content/57042

Thank you for checking the steps from the article. One more hint to try: did you register an account from the product or on Acronis website? I'd suggest testing an opposite way (register a new account on the website, if you initially did from the product or try to sign up using the in-product window). If login works , I'll help you to change the registration email in a new account.